The present invention concerns storage containers for storing diagnostic elements having a hydrophilic or hydrophilically coated surface. The present invention additionally concerns analytical measuring devices which comprise storage containers of this type, and the use of an absorption material for selectively absorbing hydrophobic, volatile substances in such storage containers.
Diagnostic elements are important components of clinically relevant analytical methods. This primarily concerns the measurement of analytes, e.g., metabolites or substrates which are determined directly or indirectly for example with the aid of a specific enzyme for the analyte. The analytes are converted with the aid of an enzyme-coenzyme complex and subsequently quantified. In this process the analyte to be determined is contacted with a suitable enzyme and a coenzyme where the enzyme is usually used in catalytic amounts. The coenzyme is physicochemically changed, e.g., oxidized or reduced by the enzymatic reaction and the process is for example detected electrochemically or photometrically. A calibration yields a direct relationship between the measured value and the concentration of the analyte to be determined.
An important criterion when preparing diagnostic elements is their ability to take up a sample containing the analyte. For this purpose, numerous commercially available diagnostic elements comprise a hydrophilic or hydrophilically coated surface which enables the test element to be wetted with the sample and allows the sample to be taken up into the test element for example by means of a sample collection element utilizing capillary effects when the diagnostic test element is contacted with a liquid sample containing the analyte.
Long-term stability has often proven to be a problem with the diagnostic test elements described above. Thus, it is known that metallic sample collection elements derived fresh from the etching bath and having a hydrophilic surface rapidly fill with aqueous liquids such as for example blood.
However, after a short period of exposure to air or after brief storage in conventional packages, the filling time of the sample collection element becomes increasingly longer and ultimately results in a complete loss of its sample take up capability. The filling time can be shortened again to the original level by treating these non-functional sample collection elements with plasma; however, the ability to take up samples is lost again within a few days.
The increasing loss of the ability of sample collection elements to take up a sample of the analyte to be determined, is due to a progressive hydrophobization of the surface of the sample collection elements which in its original state is hydrophilic or hydrophilically coated. This hydrophobization is caused by hydrophobic substances such as, for example, hydrophobic, moderately volatile organic chemical substances that come into contact with the sample collection element.
Packages for diagnostic elements which consists at least partially of plastic have proven to be particularly critical in this connection and are responsible for a significant hydrophobization of hydrophilic surfaces as a result of the slow escape of low-molecular, hydrophobic compounds from the plastic such as for example low boiling solvents or residual monomers. However, in addition to these substances which escape from packaging materials, hydrophobic volatile substances which are used in the production of the diagnostic elements that are to be stored or are formed in this process and are for example contained in the chemical coating of the test elements also result in a hydrophobization of hydrophilically coated surfaces and thus make the sample collection elements which are packaged together with the diagnostic element unusable.
If the diagnostic elements have to be sterilized before use, there is the additional problem that in general damage may be caused to the packaging or/and to the diagnostic element when for example an already packaged diagnostic element is irradiated with ionizing radiation, which subsequently can result again in the generation and release of hydrophobic volatile substances which are able to hydrophobize a hydrophilically coated sample collection element that is stored in the packaging.
In order to avoid a hydrophobization of objects having a hydrophilic surface by the packaging material and thus ensure a high degree of hydrophilicity of the surface over long storage periods, U.S. Publication No. 2009/0198119 suggests the use of a packaging which comprises at least one loose cover or/and at least one adsorbing surface in its interior, the affinity of which for apolar substances is the same as or higher than that of the hydrophilic surface of the object to be stored.
In particular, the aforesaid document envisages the use of adsorber elements or adsorber layers in the form of a hydrophilic coating, the hydrophilicity or surface energy of which is the same or higher than the hydrophilicity or surface energy of the surface of the packaged object, in order to ensure an effective adsorption of the apolar gases to the adsorber layer. In this process, the apolar gases are deposited among others on the hydrophilic surface of the adsorber element or adsorber layer which at least partially protects the hydrophilic surface of the packaged object from hydrophobization. Materials which are suitable for such hydrophilic coatings comprise for example dextran sulfate, lecithin, polyacrylic acids and polyacrylates.
However, the hydrophilic coatings used in U.S. Publication No. 2009/0198119 to adsorb apolar gases have disadvantages. Thus, the packaging described in the above document does not ensure de facto a selective adsorption of hydrophobic substances and hence ultimately cannot adequately protect against a hydrophobization of the hydrophilic surface of an object to be stored in the packaging.
In this connection, the problem arises that, on the one hand, the hydrophilic surface of the object to be stored in the packaging also hydrophobizes to a lesser or greater extent when the affinity of the adsorbing surface for apolar substances is the same as or at least not significantly higher than that of the hydrophilic surface of the object to be stored. Consequently, under such conditions the apolar gases do not preferably or exclusively adsorb to the hydrophilic surface of the adsorber element or adsorber layer.
In particular, the hydrophilic coatings described in U.S. Publication No. 2009/0198119, however, have the disadvantage that they preferably adsorb water (and not apolar gases), due to their high hydrophilicity. If the surface of the adsorber element or of the adsorber layer has a higher hydrophilicity than the surface of the packaged object, then it also has a higher affinity for water than the surface of the packaged object.
In the case of high air humidity, this results in a saturation of the surface of the adsorber element or adsorber layer with water molecules and evaporations from the packaging material can no longer be taken up by the adsorber element or by the adsorber layer, the latter resulting in depositions on the hydrophilic surface of the packaged object and thus in hydrophobization.